This invention relates generally to the field of vaccines for bacterial infections. More particularly, this invention identifies a gene that is expressed in extraintestinal isolates of Escherichia coli (E. coli), and can be used as an immunogen in vaccine formulations.
E. coli is part of the normal intestinal flora where it does not cause infections. However, infections can occur if the bacteria gain entrance to other tissues and organs. This group of E. coli strains has been designated herein as extraintestinal pathogenic Escherichia coli (ExPEC). Extraintestinal infections (EIs) due to E. coli are common in all age groups and can involve nearly any organ or anatomical site. Typical EIs include urinary tract infection (UTI), meningitis (mainly in neonates and following neurosurgery), diverse intra-abdominal infection, pneumonia (particularly in hospitalized and institutionalized patients), intra-vascular device infection, osteomyelitis, and soft tissue infection, which usually occurs in the setting of tissue compromise. Bacteremia can accompany infection at any of these sites.
Extraintestinal isolates of E. coli are responsible for the majority of urinary tract infections (UTI). Eighty to ninety percent of ambulatory UTI, 73% in individuals over 50, and 25% of nosocomial UTI are due to extraintestinal strains of E. coli. Uncomplicated urethritis or cystitis occurs most commonly. However, more severe sequelae of UTI includes pyelonephritis, intrarenal and perinephric abscess, and bacterimia with or without septic shock. Thus, it is clear that despite effective antimicrobial therapy, UTI due to E. coli causes considerable morbidity and mortality.
Although E. coli is considered to be a community-acquired pathogen, it also is the most frequently isolated gram-negative bacillus in long-term care facilities and hospitals. Severe illness and death can occur in otherwise healthy hosts, but adverse outcomes are considerably more likely in the presence of comorbid disease and impaired host defenses.
The scope and magnitude of infection caused by extraintestinal strains of E. coli is as great as any invasive bacterial pathogen. In fact, perhaps because disease due to extraintestinal isolates of E. coli is so common, the virulence and morbidity of this organism is often overlooked. As a result, extraintestinal strains of E. coli continue to be low profile xe2x80x9csilent killersxe2x80x9d imposing a medical-economic strain on the health care system.
Currently, no effective vaccine is available against ExPEC. To date, efforts to identify specific vaccine candidates against ExPEC have concentrated on virulence traits such as capsule, LPS, and pili. These studies have demonstrated that antibodies directed against these structures confer protection against homologous strains in vivo. However, the inherent marked antigenic variability of these components may limit their utility as vaccine candidates. Thus, there is an ongoing need for identification of novel effective strategies for the prevention and treatment of ExPEC infections including UTI.
The present invention is directed to identifying a gene, iroNec, from an extraintestinal isolate of E. coli. This gene was identified by transposon mutagenesis. TnphoA mutagenesis was performed on the wild type isolate of E. coli, CP9, and a library of 527 mutants with active TnphoA fusions was generated and saved. This library was subsequently screened for mutant derivatives with increased PhoA activity in the presence of urine. By this method, the iroNec gene was identified which encodes a protein of 725 amino acids. This protein has an extracytoplasmic location. DNA homology data and data demonstrating that its transcription is iron repressed supports its function as a siderophore receptor. High stringency Southern hybridization identified DNA sequences homologous to iroNec in 80-93% of ExPEC strains.
This protein or antigenic epitopes thereof can be used for inducing an immune response against extraintestinal E. coli infections. Data is presented to show that IroNec is strongly immunogenic (without adjuvant) in mice. Further, antibodies developed against IroNec were observed to be protective in a mouse intra-peritoneal challenge model. Mice immunized with IroNec had diminished mortality after intra-peritoneal challenge with the E. coli strain CP9. Additionally, there was diminished growth of the challenged strain in the liver and spleen in animals immunized with IroNec compared to non-immunized controls.
Thus, it is an object of the present invention to identify a gene, designated herein as iroNec in the extraintestinal isolates of E. coli with increased expression in human urine.
It is another object of the present invention to provide a polynucleotide that encodes the protein, IroNec.
It is another object of the present invention to provide polynucleotides that hybridize, preferably under high stringency conditions, with a polynucleotide encoding IroNec.
It is anther object of the present invention to provide peptides that are encoded by iroNec and other polynucleotides of the present invention.
It is another object of the invention to provide antigenic compositions comprising the peptides or antigenic fragments thereof for the treatment or prevention of extraintestinal infections caused by ExPEC.